The present invention relates to a damped bearing device suitable for use in high-speed rotary machines and, more particularly, to a damped bearing device for use in high-speed rotary machines which undergo several critical speeds in the course of acceleration to the high running speed.
Damped bearing devices constructed to damp the vibration generated in the rotary shaft of the rotary machine are disclosed, for example, in the specifications of U.S. Pat. Nos. 3,456,992 and 4,027,931. These damped bearing devices are constituted by a fluid film damper formed between a bearing which supports a rotary shaft and a housing, and a bearing support spring means by which the bearing is supported on the housing. The vibration in the bearing and the unstable vibration referred to as "oil whip" due to unstable oil film are damped by a combined effect of the resilient force exerted by the bearing support spring means and the squeeze action of fluid film in the fluid film damper.
In the damped bearing device of the type described above, there are an optimum damping coefficient of the fluid film damper and an optimum spring stiffness of the bearing support spring means. The optimum damping coefficient and the optimum spring stiffness are determined in accordance with the characteristics of the rotary member and the bearing.
Hitherto, the design and fabrication of the damped bearing devices have been made on the basis of the optimum damping coefficient and the spring stiffness which are determined by calculation taking into account the vibration characteristic.
It is, however, almost impossible to actually realize the expected optimum spring stiffness and optimum damping coefficient, due to various reasons such as insufficient accuracy of calculation or errors in the fabrication of parts and assembling. Particularly, it is extremely difficult to set the thickness of fluid film in the fluid film damper, so that the expected vibration damping effect can hardly be achieved.